These days, people are more and more concerned about health maintenance and promotion. Accordingly, it is desirable for health care that people can more handily obtain biological information, such as the pulse and electrocardiograms, in everyday life. In order to satisfy such a demand, for example, cellular phones including a biosensor, are being developed. By including a biosensor in a mobile device which is operated while being held with a hand, such as a cellular phone, a user is able to obtain biological information while using a regular function of the device. That is, while holding a cellular phone and performing an operation, such as inputting/selecting of a telephone number or writing email, the user is able to obtain biological information concerning the user.
However, even if a biosensor is disposed in an area where a hand contacts while a user is operating a mobile device, such as a cellular phone, parts of the user's body other than a finger used for performing an operation may move together with this finger. This may cause noise and may be contained in an output from the biosensor. In order to address such a problem, a technology for detecting body motion of a subject and removing noise produced by such body motion from a biological signal is known. Patent Document 1 discloses a pulse monitor including an acceleration sensor. This pulse monitor is worn by a subject's wrist and monitors a change in the absorbance of a subject part, so that it can calculate the pulse while the subject is walking or running. In this case, in the pulse monitor, the acceleration of an arm is detected by using the acceleration sensor, and noise produced by the motion of the arm is removed on the basis of detection results.
Patent Document 2 discloses a blood glucose meter including a pressure sensor. This glucose meter measures the absorbance of a subject part so as to calculate the blood glucose level. In this case, in this blood glucose meter, contact pressure of a subject part is detected by using the pressure sensor. If a significant change in the contact pressure due to the movement of the subject part is observed, obtained measurement data is discarded.
Patent Document 1: Japanese Patent No. 3726832
Patent Document 2: Japanese Patent No. 3767449
In order to detect and remove motion body noise, an acceleration sensor may be mounted on a mobile device, such as the pulse monitor disclosed in Patent Document 1. However, the acceleration of a mobile device and the motion (acceleration) of a hand (finger) do not necessary coincide with each other. More specifically, if a mobile device is held with a hand and is operated with a finger, a user may operate the mobile device almost without moving the mobile device but only by moving a finger. In this case, it is difficult to detect and remove motion body noise by using an acceleration sensor.
Alternatively, in order to detect and remove body motion noise, a pressure sensor may be used. However, when an electrocardiogram sensor or a temperature sensor is used as a biosensor, even if contact pressure is changed, a high level of noise is unlikely to occur, which may lead to incorrect detection. Additionally, the provision of an acceleration sensor, a pressure sensor, or a sensor specially used for detecting body motion unfavorably increases the cost of a mobile device.